Lemme think...
hmmm, my favorites are:
Jolteon, Vaporeon, Flareon, Umbreon, Espeon, Leafeon oh and don't forget Glaceon. Wait, that's all of them right?
/facepalm
Actually I have no favorites when it comes to Eeveelutions, I just like the Eevee family. Eevee has the best evolution tree ever. ;)